There has been used a control unit constituting a controller for an ignition system, an injection system for an internal combustion engine or the like, in which a unit body including a printed circuit board and components mounted on the printed circuit board is resin-molded in order to provide water proofing and vibration proofing property to the control unit.
In the case where a component constituting a unit body does not have an exposure required portion which is required for being exposed to outside while the component is used, the unit body may be covered with a resin-molded portion. However, in the case where components such as a pressure sensor, a variable impedance element (for example, a variable resistor) having an operation knob, and a display device having a indicator such as a liquid crystal display board are included in a component constituting a unit body, an exposure required portion of these components is required not to be covered with the molded portion.
The exposure required portion of the pressure sensor is a pressure introducing portion having a hole for introducing a detected pressure to a sensor, and the exposure required portion of the variable impedance element is an operation knob which is controlled when impedance is adjusted. The exposure required portion of the display device is an indicator such as a liquid-crystal display device.
In Japanese Patent Application Laid-Open Publication Nos. 7-221429 and 2001-152906, there are proposed mold-type electronic control units in which a unit body including a specific component having an exposure required portion on a printed circuit board is covered with a resin molded portion.
In the mold-type electronic control unit, a specific component having an exposure required portion is housed in a component case, and the component case is mounted to a printed circuit board together with other components. Then, the printed circuit board is inserted into a sheathing case, and thermosetting resin such as epoxy resin or polyurethane resin is poured into the sheathing case until a lead terminal of the component is hidden to form a molded portion.
However, there have been problems as described below in the mold-type electronic control unit shown in Japanese Patent Application Laid-Open Publication Nos. 7-221429 or 2001-152906.    (a) Many components are needed since a sheathing case is required, which causes the cost to be increased.    (b) A number of manufacturing steps is increased since a step for fixing a printed circuit board to the sheathing case is required, which causes the cost to be increased.    (c) It takes time to cure resin since thermosetting resin is used, which requires long manufacturing time.    (d) A thermostatic oven is needed for curing the thermosetting resin, which causes the cost for manufacturing facilities to be increased.    (e) Since the components are exposed to high temperature when pouring the thermosetting resin into the sheathing case, the components are likely to be deteriorate or broken.    (f) The electronic control unit can not be recycled since the thermosetting resin is used.
The above problems may be solved by forming a molded portion by injection molding; however, in the case where components being attached to a printed circuit board include a specific component having an exposure required portion, a special consideration is necessary so that the exposure required portion of the specific component is not covered with the molded portion.